part 1: vascular and neural - harvard university

2010Copyright @ American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.

Clinical Sonopathology for the Regional AnesthesiologistPart 1: Vascular and Neural

Brian D. Sites, MD,* Alan J.R. Macfarlane, MBChB, MRCP, FRCA,Þ Vincent R. Sites, MD,þAli M. Naraghi, MD, FRCR,§ Vincent W.S. Chan, MD, FRCPC,|| John G. Antonakakis, MD,¶

Mandeep Singh, MBBS, MD,|| and Richard Brull, MD, FRCPC||

Abstract: The use of ultrasound to facilitate regional anesthesia is anevolving area of clinical, education, and research interests. As ourcommunity’s experience grows, it has become evident that anesthesiol-ogists performing Broutine[ ultrasound-guided blocks may very well beconfronted with atypical or even pathologic anatomy. As an educationalresource for anesthesiologists, the following articles present examples ofcommon sonopathology that may be encountered during ultrasound-guided regional anesthesia. This present article describes sonopathologyrelated to blood vessels and nerves.

(Reg Anesth Pain Med 2010;35: 272Y280)

W hen an anesthesiologist scans a patient with ultrasoundduring the performance of a peripheral nerve block, there

is a distinct possibility that a Btextbook image[ will not be pre-sent. Nerves and key reference structures may be hard to dis-tinguish from surrounding soft tissues. There are many potentialreasons for this including the laws of physics (eg, artifacts),incorrect machine settings, nuances of patient anatomy, incorrectscanning techniques, and pathologic conditions. Many of theeducational objectives and training efforts occurring on nationaland international levels focus on image optimization throughBknobology[ issues and scanning techniques. However, little in-formation exists in the literature describing abnormal findings thatmay be encountered during the conduct of ultrasound-guidedregional anesthesia (UGRA). Such pathology or atypical anatomyas seen with ultrasound is referred hereon as sonopathology.

This 2-part article presents a collection of sonopathologythat was acquired during a 7-year period at 5 separate insti-tutions. Part 1 addresses common pathologic conditions affect-ing the tissues most central to UGRA; that is, blood vessels andnerves. Part 2 describes important pathology related to sur-rounding structures including the viscera and subcutaneous

tissues. The information can be considered an extension ofthe content offered in the 2 articles previously published onultrasound-related artifacts.1,2 The primary objective was to ex-pand the educational resources available to anesthesiologists par-ticipating in UGRA. The cases and discussions provided in thearticle will hopefully support the notion that anatomic variationand pathology do occur and will be encountered within the con-text of our scope of practice. The authors do not support the use ofultrasound as a mass screening examination by anesthesiologists.We recognize that not every case presented in the article will beseen or be relevant to all practitioners. We do believe, however,that the identification of abnormal tissue or challenging anatomypresents a distinct opportunity for anesthesiologists to alter theanesthetic plan, contribute to the medical care of the patient, andpotentially avoid certain complications.

VASCULARBlood vessels are commonly used as landmarks for UGRA.

Short-axis imaging of blood vessels reveals round anechoicstructures that are either pulsatile (arteries) or compressible(veins). Blood vessels are generally easy to identify and the targetnerve(s) usually lie in close proximity. Vascular lesions, however,can create difficulties for the anesthesiologist either by impedingthe intended needle trajectory to the nerve or by displacing thenerve.3 Both intravascular and perivascular pathology may beencountered during preprocedural scanning. Color Dopplerimaging complements 2-dimensional findings and can help todetermine patency, vessel narrowing, and perturbations in bloodflow. The identification of vascular pathology may have importantimplications for anesthetic management.

AtherosclerosisAtherosclerosis affects up to 10% of the Western popula-

tion older than 65 years, although the true incidence is difficultto quantify because it is often asymptomatic. Up to 10% ofadults older than 80 years have greater than 50% carotid arterystenosis.4 The carotid bifurcation, the most common site forcarotid plaques, occurs at the level of the thyroid cartilage.Plaques are often calcified and, therefore, may create distinctacoustic dropout shadows (Fig. 1). Some plaques may behypoechoic and only noticeable if there is an area absent ofcolor flow within the vessel circumference. Plaques that appearecholucent are lipid-rich, whereas echogenic plaques have ahigher content of fibrous tissue and calcification. Diagnosticscanning for plaques is generally performed using vascular long-axis imaging to search for a stenotic lesion along the length ofthe vessel. Short-axis scanning, as is performed for interscaleneblocks, still allows for detection of an eccentric plaque. In thelower limb, the superficial femoral artery (Figs. 2 and 3) is themost common location for atherosclerosis, with poplitealatherosclerotic disease being less prevalent.5

ULTRASOUND ARTICLE

272 Regional Anesthesia and Pain Medicine & Volume 35, Number 3, May-June 2010

From the *Department of Anesthesiology, Dartmouth-Hitchcock MedicalCenter, Lebanon, NH; †Department of Anaesthesia, Glasgow RoyalInfirmary, Scotland, UK; ‡Department of Radiology, Lahey Clinic,Burlington, MA; §Joint Department of Medical Imaging of UniversityHealth Network and Mount Sinai Hospital, Toronto Western Hospital,Toronto, Ontario, Canada; ||Department of Anesthesia and Pain Manage-ment, Toronto Western Hospital, University Health Network, Toronto,Ontario, Canada; and ¶Department of Anesthesiology, University of Virginia,Charlottesville, VA.Accepted for publication August 8, 2009.Address correspondence to: Richard Brull, MD, FRCPC, Department

of Anesthesia and Pain Management, Toronto Western Hospital,399 Bathurst St, Toronto, Ontario, Canada M5T 2S8(e-mail: [email protected]).

The authors did not receive funding for this study and have no conflict ofinterest to declare.

Copyright * 2010 by American Society of Regional Anesthesia and PainMedicine

ISSN: 1098-7339DOI: 10.1097/AAP.0b013e3181ddd1f8


Carotid thrombosis can complicate a preexisting athero-sclerotic plaque, as seen in Figure 4. Of note, the thrombosisis not fully appreciated until the operator transitions from theshort-axis view (Fig. 4A) to the long-axis view (Fig. 4B). Arte-rial thrombosis tends to appear homogenous and hyperechoic.However, thrombosis is usually less echogenic than calcium-rich plaques. This difference is clearly evident by comparingFigures 1 and 4B.

Figure 5 is an example of a Doppler phenomenon calledaliasing. Aliasing can be identified when using color Doppler inareas of stenosis that generate turbulent and high-velocity flows.Aliasing appears as a mosaic of colors representing flow thatexceeds the scale set on the ultrasound machine. Aliasing can bea distinct clue that there is vascular pathology present.

Formal quantification of vascular stenosis by ultrasound ishighly accurate and involves standard 2-dimensional imaging,

analysis of Doppler waveform, and blood velocity measure-ments.6 Ultrasound can also provide information on plaquemorphology, giving insight into the risk of embolism (ie, mobileplaque).

The incidental detection of both femoral and carotid arterialplaques has already been reported during scanning for femoraland interscalene nerve blocks, respectively.7 In each instance,the anesthetic and/or surgical management was altered. Figure 1is an example of a carotid plaque incidentally found during theperformance of an interscalene block. The detection of this lesionin a hypertensive patient scheduled for shoulder surgery resultedin cancellation with a view to improving blood pressure controland arranging a formal investigation. The case later proceededwith invasive arterial monitoring, strict perioperative blood pres-sure control, altered patient positioning, and the use of intraop-erative electroencephalography monitoring. In another example,on detecting a femoral artery plaque in a patient presenting fortotal knee arthroplasty, it was jointly decided by the surgery andanesthesia teams not to use a tourniquet during the procedure.7

The most useful (and simplest) clue for the anesthesiologistindicating the presence of vascular pathology is the identifica-tion of a hyperechoic area within the lumen of a blood vessel thatis associated with a dropout shadow. If a dropout shadow isnoted, consider changing the machine settings from a muscu-loskeletal application to a vascular-specific setting and loweringthe gain to help reduce artifactual speckles within the vessellumen. These adjustments may help to exclude a false-positive

FIGURE 2. Short-axis image demonstrating a thrombus at thebifurcation of the common femoral artery. PA indicatesprofundus artery; SFA, superficial femoral artery. The plus signsin the image are from the sonographer using machine calipersoftware to make precise vessel diameter measurements. Thrombitend not to be as dramatic when imaged in short-axis incomparison to the long-axis (Fig. 3).

FIGURE 3. A, Long-axis image demonstrating obstruction to flowat the bifurcation of the right common femoral artery. Noticethe abrupt ceasing of blood flow as displayed by color Dopplerat the SFA/CFA junction and within the profundus. CFA indicatescommon femoral artery. B, Reconstructed 3-dimensionalcomputed topography (CT) angiogram confirming the findingsof the ultrasound examination.

FIGURE 1. Long-axis image of the common carotid artery duringthe performance of an interscalene block. The anesthesiologistsincidentally noticed the hyperechoic lesion just proximal to thecarotid bulb. Notice the distinct acoustic dropout shadow createdby the calcified plaque.

FIGURE 4. A, Short-axis image demonstrating a thrombus in thecommon carotid artery (CCA). B, Long-axis image of the sameCCA demonstrating the extent of the thrombus.

Regional Anesthesia and Pain Medicine & Volume 35, Number 3, May-June 2010 Sonopathology Part 1

* 2010 American Society of Regional Anesthesia and Pain Medicine 273


diagnosis of a vessel lesion. Also, long-axis imaging of sus-pected vascular pathology will provide more information thanthe standard short-axis view.

Deep Venous ThrombosisThe venous drainage system of the lower limb consists of

the superficial (great and small saphenous veins) and the deep

(tibial, peroneal, popliteal, and femoral veins) systems, con-nected by perforating and transfascial veins. The incidence ofdeep venous thrombosis (DVT) varies between particular patientpopulations.8 The femoral and popliteal deep veins are commonlyimaged by anesthesiologists and can contain acute thrombi.9

Classically, a venous thrombus presents (in short-axis) as a non-compressible and often dilated circle of variable echogenicity.There will likely be an absent or obstructed blood flow.10 Sono-graphic findings will change depending on the age of thethrombosis. In general, a fresh thrombus is hypoechoic and ho-mogenous with an associated dilated, incompressible vein. Achronic thrombus may shrink and become more hyperechoicand heterogeneous.

The incidental finding of a DVT during ultrasound scan-ning for regional anesthesia has already been documented.7,11

In 1 case, an inferior vena cava filter was inserted before sur-gery.11 Figure 6 demonstrates a dramatic thrombosis of thecommon femoral vein as seen in long-axis imaging. This DVT

FIGURE 5. Long-axis view demonstrating the obstruction toblood flow in the internal carotid artery causing aliasing on colorDoppler. Aliasing can be a sign that indicates turbulent andhigh-velocity flow associated with a stenosis. This carotid artery isalso being analyzed with pulse wave Doppler. Pulse waveDoppler simply measures blood flow velocity at a particular pointas indicated by the cursor on the screen that the operatorcould move. The velocities instead of being mapped with color(color Doppler) are presented as a spectral display (bottom partof image). In such a spectral display, the x-axis is time and they-axis is velocity in centimeters per second (cm/sec).

FIGURE 6. Long-axis image demonstrating a large thrombusextending from the superficial femoral vein to the commonfemoral vein. CFV indicates common femoral vein; PFV, profundusfemoral vein; SFV, superficial femoral vein.

FIGURE 7. Doppler analysis of the same patient as in Figure 6.This image demonstrates obstruction to blood flow as suggestedby color Doppler. The large thrombus is evident, extendingfrom the superficial to the common femoral vein.

FIGURE 8. Venous thrombus in the SFV. Notice the lack ofvessel compressibility and absent blood flow with Doppleranalysis. Lack of dynamic compressibility with the transducerduring ultrasound analysis is considered a hallmark of a DVT.

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274 * 2010 American Society of Regional Anesthesia and Pain Medicine


has extended proximally from the superficial femoral vein to thecommon femoral vein. Doppler analysis can help confirm thelack of blood flow secondary to an obstruction (Fig. 7).

Noncompressibility (Fig. 8) or intraluminal echogenicityare features of DVT that will likely be most evident duringscanning for regional anesthesia. If suspicion exists that athrombus is present, scanning with color Doppler may be helpfulin identifying obstruction to or absent blood flow. The anes-thesiologist must be mindful of the limitations and artifactsrelated to color Doppler.1,2 Most importantly, the Doppler equa-tion precludes the detection of blood flow when the angle ofincidence of the ultrasound beam is 90 degrees.1,2 Further, whenanalyzing low-velocity structures such as the superficial fem-

oral vein, the velocity scale should be turned down. In the caseprovided (Fig. 7), the scale was set at 11 cm/sec to evaluatevenous flow. In the case of the carotid artery, velocity scaleswill need to be set higher (30 cm/sec) to help prevent aliasing(see above).

AneurysmsExcluding the aorta, the reported incidence of peripheral

aneurysms in hospitalized patients is only 0.007%.12,13 How-ever, peripheral aneurysms most commonly occur in the pop-liteal artery as shown in Figure 9. The femoral artery, visualizedwhen locating the femoral nerve, is less frequently involved withaneurismal disease. Aneurysms are saccular or spindle-shaped

FIGURE 9. Popliteal aneurysm. A, Normal popliteal artery approximately 5 cm proximal to the popliteal crease. B, Short-axis imageof an aneurysm in the same patient at the level of the popliteal crease. This lesion could easily be detected in the context ofperforming a popliteal sciatic block.4 PA indicates popliteal artery. The plus signs are part of themachine software used by the sonographerto measure vessel diameter.

FIGURE 10. Elevated central venous pressure. A, Represents the normal situation in which the subclavian artery is the only visualizedvascular structure during a supraclavicular block. B, Represents a dilated subclavian vein looping anterior to the supraclavicular brachialplexus and the subclavian artery. SCA indicates subclavian artery; SCV, subclavian vein. This lesion was identified while imaging for asupraclavicular nerve block. This lesion reflects elevated central venous pressure likely related to tricuspid regurgitation. Normally, thesubclavian vein is not seen while imaging in the supraclavicular fossa for a brachial plexus block. Screen right in both images representsa medial/anterior direction.




dilatations of the vessel lumen. Ultrasound examination is theinitial investigation of choice and can reveal information ondiameter, as well as the presence of thrombosis. False orpseudoaneurysms occur in up to 4% of cases after percutaneoustransluminal angioplasty.14 Aneurysms can be differentiatedfrom other perivascular hypoechoic structures such as hemato-ma, seroma, or lymphocele by the bidirectional Bto and fro[ flowthrough the neck of the aneurysm, as visualized best by colorDoppler.15

Elevated Central Venous PressureThe internal jugular vein is commonly imaged during

brachial plexus blockade above the clavicle. Raised centralvenous pressure occurs in a variety of pathologic conditions andmay be noticed in the internal jugular or even subclavian veinduring an interscalene or supraclavicular block. Figure 10B isan example of a dilated subclavian vein that is looping anterior

to the supraclavicular brachial plexus in a patient with tricuspidregurgitation, chronic right-sided heart failure, and elevatedcentral venous pressure. Given that the transducer was posi-tioned in the supraclavicular fossa, a supraclavicular nerve blockwould be technically challenging, with a higher risk of vesselpuncture, hematoma formation, and possible intravascularinjection. It should be noted that in the standard view for asupraclavicular block (as in this example), the subclavian veinis usually not visualized.

FIGURE 13. ‘‘Rainbow’’ arrangement of the supraclavicularbrachial plexus. This is a short-axis image of the subclavian artery(SA), pleura, and the first rib. In this patient, the neuralstructures (likely the divisions and cords) are seen surroundingthe subclavian artery in a rainbow-like fashion. That is, they arelocated on either side (medial and lateral) as well as superiorly.Arrows indicate the individual neural elements. Classically, thebrachial plexus lies lateral to the subclavian artery (Fig. 10A).The authors believe that the appreciation and identification ofsuch neural variation will likely improve the quality of the block.

FIGURE 14. Atypical femoral nerve. This is a case of the femoralnerve that appears to be embedded in the iliopsoas muscle.Classically, the femoral nerve is an oval structure that is foundunder the fascia iliaca and adjacent to the iliopsoas muscle. Itwould be reasonable to conclude that an injection extramuscularlymay result in a suboptimal block. FA indicates femoral artery;FI, fascia iliaca; FN, femoral nerve; IPM, iliopsoas muscle.

FIGURE 11. Unintentional puncture of a branch of the subclavianartery. The needle is seen through and through a structurebelieved to be the transverse cervical artery. This puncture resultedin a postsupraclavicular block hematoma that was controlledwith compression. SA indicates subclavian artery, and thetriangles mark the long-axis view of the transverse cervical artery.The arrow indicates the needle puncturing the transversecervical artery.

FIGURE 12. Atypical location of the brachial plexus. This imagedepicts the brachial plexus in the midneck crossing directlythrough the anterior scalene muscle. Notice that the ‘‘empty’’interscalene groove is located just posteriolateral to the actualnerves. The anesthesiologist recognized this variant anatomyand performed the injection into the anterior scalene muscle.AS indicates anterior scalene muscle; BP, brachial plexus (roots);MS, middle scalene muscle.




Vascular AnatomyIt should be noted that normal anatomic variation in blood

vessels can also create an obstacle to needle insertion andsuccessful block placement. Examples of typical vascularvariations that may impede typical needle approaches wouldinclude the dorsal scapular artery and the transverse cervicalartery in the brachial plexus blocks above the clavicle. In thelower extremity, the lateral femoral circumflex artery can be achallenge to avoid during the performance of femoral nerveblocks. Figure 11 depicts an unintentional puncture of what ispresumed to be a large transverse cervical artery during asupraclavicular block. This puncture resulted in a postprocedurehematoma that was controlled with compression. This caseemphasizes the importance of conducting a prepuncture scanwith color Doppler.

NERVESUltrasound can now rival magnetic resonance imaging as

an imaging modality for peripheral nerves.16 Nerves can behypoechoic or hyperechoic depending on the nature of thesurrounding tissue and the amount of connective tissue withinthe nerve itself.17 Most often, a honeycomb pattern is evident inthe short-axis view, with hypoechoic nerve fascicles surroundedby the echogenic epineurium.

A variety of relatively common pathologies such ashereditary neuropathies, nerve compression, nerve entrapment,rheumatologic disorders, infectious disorders, nerve tumors,intraneural ganglia, and anatomic variants may be encounteredduring the conduct of UGRA. If intrinsic or extrinsic nerveabnormalities are encountered, an alternative anesthetic man-agement should be considered because neural pathology is arelative contraindication to nerve blockade.18 Perioperativenerve injury is a complex and multifactorial process. The useof ultrasound guidance does not necessarily prevent or reducethe incidence of nerve injury.19,20

Anatomic VariantsNeural anatomic variants are commonplace, potentially

undermining the success of UGRA. For example, the anatomy ofthe upper nerve roots of the brachial plexus is anomalous in 13%to 35% of cases.21Y23 Figure 12 demonstrates neural tissuedirectly penetrating the anterior scalene muscle of an 80-year-old man presenting for a rotator cuff repair. Of note, the in-terscalene groove has no neural tissue present and is easy toidentify just posteriolateral to the anterior scalene muscle.

The resurgence in popularity of supraclavicular blockadeand the recent description of the Bcorner-pocket[ ultrasound-guided technique24 rely on the normal location of the divisionsof the brachial plexus immediately lateral to the subclavianartery and above the first rib. Anomalous nerve locations cancompromise the success and safety of ultrasound-guidedsupraclavicular techniques (Fig. 13).25 Variations in the anatomyof the cords and nerves relative to the axillary artery are alsowell recognized.26

Reports of anomalous nerve anatomy in the lower extremityare less common, possibly reflecting the scope of modernregional anesthetic practice. Nonetheless, Figure 14 demon-strates a case of what we believe to be the femoral nerve em-bedded in the iliopsoas muscle. Classically, the femoral nervedivides into the anterior and posterior divisions below theinguinal ligament.27 Descriptions, however, do exist of thisbranching occurring more proximally, above the inguinalligament.28 In 1 cadaver study, psoas or iliacus muscle slipswere noted to cover the femoral nerve in 7.9% of cases.29

Inflammatory NeuritisCompressions by hematoma or trauma from a retractor are

the most common causes of perioperative inflammatory neuritis,but other mechanisms include sepsis and intraoperative limbpositioning. The incidence of femoral nerve palsy after total hiparthroplasty is less common than sciatic nerve injury, and thishas been reported to be 0.7%.30 Figure 15 depicts a femoral

FIGURE 15. Femoral neuropathy. These are short-axis imagesof the infrainguinal femoral nerve that come from the samepatient. A, Normal right-sided femoral nerve. B, Swollen andenlarged left femoral nerve. This patient sustained a dramaticfemoral neuropathy after a total hip revision on the left side.The patient was having an ultrasound examination by a radiologistas part of a comprehensive diagnostic evaluation. The dottedline in each image outlines the femoral nerve as seen by theradiologist. The decision where to draw this line may seemarbitrary to some readers. However, the line was drawn basedon the observed presence of a fascicular pattern (internalhypoechoic circles). This pattern is clearly evident within thetracing and absent adjacent to it.

FIGURE 16. Swollen sciatic nerve. This is a short-axis image ofan enlarged sciatic nerve with swollen fascicles in a patient witha diabetic peripheral neuropathy. The image was acquiredapproximately 5 cm proximal to the popliteal crease. Theanesthetic plan for this patient was a combined sciatic andproximal saphenous nerve block to act as a surgical anestheticfor a below-the-knee guillotine amputation. The anesthesiologistrecognized the abnormal nerve before the injection. However,given the potential morbidity of a general anesthetic (secondary tothe patient’s severe cardiopulmonary disease), the decision wasmade to proceed with the block. The decision where to drawthe nerve outline is supported by the same process as describedfor Figure 15. In addition, the hypoechoic adipose tissuesurrounding the sciatic nerve clearly demarcates the boarder ofthe neural tissue.




nerve of a patient who developed a left-sided femoral nervepalsy after a total hip arthroplasty. The nerve appears swollenand enlarged, particularly when compared with the contralateralside. Postoperatively, the patient developed a dense motor deficitof the quadriceps muscle, as well as sensory loss in the anteriorthigh and knee. It is important to note that this patient did notreceive a femoral nerve block.

If an abnormality in the target nerve is suspected, scan thecontralateral side as a control. If swelling or distorted archi-tecture is identified, there is significant chance that the nerveis abnormal. Careful thought should be given to altering theanesthetic plan. Figure 16 demonstrates an enlarged sciaticnerve as imaged 5 cm proximal to the popliteal crease in apatient with diabetes with known peripheral neuropathy. In thisimage, swollen fascicles are noted with a grossly abnormaldiameter. Given this patient’s severe concomitant cardiopulmo-nary condition, a decision was made to still proceed with thenerve block as a surgical anesthetic for a below-the-kneeamputation.

Nerve TumorsPeripheral nerve tumors are infrequent in comparison with

other primary neurologic tumors.31,32 Indeed, malignant tumorshave an incidence of only 0.1 per 100,000.33 Both schwanno-mas and neurofibromas can be detected by ultrasound, althoughit is difficult to distinguish between these 2 pathologies.34 Inboth cases, hypoechoic masses may be seen originating fromthe nerves, sometimes with posterior acoustic enhancement .Figure 17 represents a dramatic example of a large schwannomaoriginating from the sciatic nerve in the popliteal fossa. In thisparticular patient, the anesthesiologist was requested by thesurgeons to help identify an incision site that would providedirect access to the middle of the tumor.

Neurofibromas can sometimes have hyperechoic tissuelayers, which, when alternating with hypoechoic layers, create aBtarget[ sign. Other masses such as hemangiomas, lymphomas,and ganglia may also develop inside nerves. Nonneural tumors

may also invade peripheral nerves. Ultrasound can help to defineits size and its relationship to the surrounding tissue and mayalso be used for needle-guided biopsy.34

Nerve EntrapmentNerves are generally compressible and alter their shape

depending on the volume of the anatomic space that theytraverse. Although short periods of compression usually produceonly a temporary neuropraxia, prolonged severe pressure candistort the nerve architecture. Extrinsic compression of a nervemay occur anywhere in the body. Nerve flattening, with fusiformswelling of the nerve proximal to the lesion, may be encounteredon ultrasound imaging. In such entrapment neuropathies, thenerve may also become hypoechoic at and proximal to thecompression site. This loss of echogenicity occurs because ofswelling of the fascicles and decreased echogenicity of theepineurium.35 Figure 18B demonstrates the lateral antebrachialcutaneous (LABC) nerve of a patient who presented with aneuropathic syndrome of his anterior lateral forearm. Lateralantebrachial cutaneous nerve entrapment is a diagnosis, which,in such circumstances, should be considered.36 This patient wasreferred to one of the authors by a plastic surgeon, requesting atrial block of this nerve in the antecubital fossa. The goal was todiagnose a lesion at this level. By tracing distally from themusculocutaneous nerve in the axilla (Fig. 18A), the LABC wasfound. In the author’s experience, the nerve appeared fusiform

FIGURE 18. Lateral antecubital brachial cutaneous neuropathy.The patient was experiencing a chronic pain syndrome involvingthe entrapment of this the LABC nerve. A, High-resolutionshort-axis image of the musculocutaneous nerve (MCN) in theproximal arm. This nerve was followed distally until the LABCnerve was seen branching off. B, Arrows indicate the fusiformLABC nerve imaged approximately 2 cm proximal to theantecubital fossa. In the author’s experience, this nerve appearedswollen and larger than expected.

FIGURE 17. Schwannoma. This image displays the operativedissection of this large benign peripheral nerve tumor originatingfrom the sciatic nerve. The corresponding short-axis ultrasoundimages andmagnetic resonance image are provided as references.The tumor images are the large heterogeneous and mostlyhypoechoic circles indicated by the arrows. In this particular case,the ultrasound examination was conducted intraoperatively tohelp assist the surgeons in making the most effective incision andto confirm that all the tumor was resected. F indicates femur.




and swollen. An injection of local anesthetic around the nerveresulted in relief of the neuropathic pain and so a decision wasmade to proceed to decompressive surgery. Intraoperatively,however, the surgeons could not find the LABC nerve. There-fore, under ultrasound guidance, a spinal needle was insertednext to the nerve (Fig. 19). With this guidance, the surgeonswere able to dissect a small fascial band from the nerve. Post-operatively, the patient was pain-free.

In summary, part 1 examined common pathologic condi-tions affecting the tissues critically involved with UGRA: bloodvessels and nerves. Part 2 will expand our discussion of sono-pathology to include interesting cases associated with bone,viscera, subcutaneous tissue, and foreign bodies. As in part 1, weemphasize potential clinical connections to anesthesiologistspracticing regional anesthesia.

ACKNOWLEDGMENTSThe authors thank Mr Liang Liang, BMSc, Research

Fellow, Department of Anesthesia, Toronto Western Hospital,Toronto, for his assistance in formatting and editing of imagesduring the preparation of the article.

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FIGURE 19. Operative dissection. A, Incorrect markings that thesurgeons made before skin incision. The surgeons were unableto find the nerve using these surface landmarks. The LABC nervewas actually more medial. B, The anesthesiologists usedultrasound to identify the nerve and placed a 22-gauge spinalneedle adjacent to it. The surgeons dissected along the needle andsuccessfully found the LABC nerve.




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part 1: vascular and neural - harvard university

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